'99 379 rear airbag height.

You should be able to play with the leveling valve and set the height wherever you want. I set mine at 13'6 1/2 when pulling van trailer. Reason it's not set at 13'6 even is I have tall rubber so I need the extra 1/2 in for trailer clearance over tires. If you loosen the retainer nut on the valve arm and it doesn't release air out of bags then the valve is busted. Also if it has been cold in your area they have a tendency to freeze up, sometimes once they freeze they do not work properly ever again. They are mostly constructed of hard plastic, if the plastic cracks or warps they don't let air flow through them anymore.

 

Air bags can be adjusted easily. But your heavy spec truck might just might sit too high for a van.
Don't take a mechanics word for the ride height.
I had a new leveling valve installed at Council Bluffs IA Peterbilt. The mechanic had it jacked up. I backed out of the door and immediately adjusted it down.
They worked on alot of 379's there and do 90 percent of the work right. I just took care of it myself.
My terminal was right up the road. Went there if I could.

 

Can't you rotate the valve itself? Mine has slotted holes so you can rotate the valve. That changes the height. I had the solid link for years until the rubber rotted out so bad it had to be changed. When you set the ride height. Set it at the back axle. Then check the front axle for clearance to the frame and how much travel you have before it bottoms out on the frame.

 

I meant where the valve bolts to the frame bracket. It should be a good sized L shaped bracket that hangs off the left frame rail.

 

You adjust the valve itself. There should be a nut on the arm coming out of the valve, loosen the nut then adjust the platic piece behind the arm up or down, then tighten the nut back up

 

Mine is doing the same thing. I know what your talking about and everyone's comments are not answering your question. The back airbags are aired up more than front. Only one leveling valve exist. The frame angles down in the front. Does not set level. Front spacers are correct and good springs. With air suspension dropped only front drive sets on rest and bottoms out shocks while back axle looks like it still is aired up, but bags are deflated and soft and sets about 6 inches from resting on stops. Like back is jacked teter totting on front axle. Throwing the rear driveline out. Put air to it and both air up but not as much on front axle. Torque bar on back sets horizontally while front sets at an angle do to steer dropped down. All airbags are same. Confused! Help

 

Forgive me if I missed you saying it, but what suspension do you have? Air leaf, air trac, or...?